How Can cold And Fever Along With Throat Infection Be Treated?

my son is 3 year old and repeatively suffer from cold and fever mostly due to throat infection. Secondly he has runny nose kind of something is troubling while breathing but nostril has nothing in them We consulted pediatric which said it is cold which in inside and has no running nose. for which dr prescribed sinarest pd nasal drops and monticope for 2 months but we observed occasionally he has running nose . over all he is not improving with cold even after regular dose of monticope and sinarest pd. kindly suggest what should we do for noisy breathing Dr advised him for flu vaccine also but when to yake for flu vaccine because he is not getting alright have mild running nose in this condition shall we go for flu vaccine